Present-day velocity and stress fields of the Amurian Plate from thin-shell finite-element modelling

Abstract

Most numerical models of Asian deformation focus on rapidly deforming zones close to the Indian indenter, and seldom extend to its northern 'deformation front'. In this study, we examine the present-day deformation of the Amurian continental plate (northeast Asia) which faces stable Eurasia along the Baikal-Stanovoy boundary. The present-day velocity and stress fields of the Amurian Plate are reproduced by means of thin-shell finite-element modelling. We first compile available GPS and focal mechanism data in and around the Amurian Plate in order to characterize the nature and geometry of its boundaries and its relative velocity with respect to adjacent plates. We then use the finite-element code SHELLS to model the plate deformation under different boundary conditions. Plate rheology, thermal state and crust and mantle thicknesses are fixed according to existing data. We first test the influence of body forces due to crustal thickness variations; then, we test the role of far-field conditions imposed by indentation and extrusion processes to the south, and subduction to the east. Our best-fitting model shows the following. (1) Assuming a relatively 'strong' classical mantle rheology, body forces play a minor role in plate deformation, since they predict velocities much smaller than boundary forces. (2) Transition from south-north compression in the west, to west-east extrusion in the east along the southern plate boundary satisfyingly explains the velocity and stress fields of the Mongolia-Baikal region, suggesting that extrusion is the dominant driving force of the Baikal rift opening. (3) A low-friction fault with null relative Okhotsk-Eurasia and Philippine Sea-Eurasia velocities along the eastern plate limit explain observed stresses and velocities in Sakhalin and Japan, suggesting that eastern subduction processes do not play a major role in long-term plate deformation. © 2004 RAS.